Skeletal System

Skeletal System

Parts of the Skeletal System

• Bones (skeleton)• Joints• Cartilages• Ligaments

Subdivisions of Skeleton

• Axial skeleton• Appendicular skeleton

Functions of Bones

• Support the body• Protect soft organs• Allow movement due to attached

skeletal muscles• Store minerals and fats• Blood cell formation

Bones of the Human Body

• The adult skeleton has 206 bones• Two basic types of bone tissue–Compact bone - homogeneous–Spongy bone• Small needle-like pieces of bone•Many open spaces

Classification of Bone on the Basis of Shape

• Long bones–Typically longer than they are wide–Have a shaft with heads at both ends–Contain mostly compact bone–Example: femur, humerus


• Short bones–Generally cube-shape–Contain mostly spongy bone–Example: carpals, tarsals


• Flat bones–Thin, flattened, and usually curved–Two thin layers of compact bone

surround a layer of spongy bone–Example: skull, ribs, sternum


• Irregular bones–Irregular shape–Do not fit into other bone

classification categories–Example: vertebrae, hip bones

Types of Bones

Anatomy of a Long Bone

• Diaphysis–Shaft–Composed of compact bone

• Epiphysis –Ends of the bone–Composed mostly of spongy bone


• Periosteum–Outside covering of the diaphysis–Fibrous connective tissue membrane

• Sharpey’s fibers - secure periosteum to underlying bone

• Arteries - supply bone cells with nutrients


• Articular cartilage–Covers the external surface of the

epiphyses–Made of hyaline cartilage–Decreases friction at joint surfaces


• Epiphyseal plate - flat plate of hyaline cartilage seen in young, growing bone

• Epiphyseal line–Remnant of the epiphyseal plate–Seen in adult bones


• Medullary cavity –Cavity inside of the shaft–Contains yellow marrow (mostly fat)

in adults–Contains red marrow (for blood cell

formation) in infants

Parts of a Long Bone

Bone Markings

• Surface features of bones–Sites of attachments for muscles,

tendons, and ligaments–Passages for nerves and blood vessels

• Categories of bone markings–Projections or processes—grow out from

the bone surface–Depressions or cavities—indentations

Microscopic Anatomy of Bone

• Osteon (Haversian system) - a unit of bone containing central canal and matrix rings

• Central (Haversian) canal–Opening in the center of an osteon–Carries blood vessels and nerves

• Perforating (Volkman’s) canal–Canal perpendicular to the central canal–Carries blood vessels and nerves


• Lacunae–Cavities containing bone cells

(osteocytes)–Arranged in concentric rings

• Lamellae–Rings around the central canal–Sites of lacunae


• Canaliculi –Tiny canals–Radiate from the central canal to lacunae–Form a transport system connecting all

bone cells to a nutrient supply

Formation of the Human Skelton

• In embryos, the skeleton is primarily hyaline cartilage

• During development, much of this cartilage is replaced by bone

• Cartilage remains in isolated areas–Bridge of the nose–Parts of ribs–Joints

Bone Growth (Ossification)• Epiphyseal plates allow for lengthwise growth

of long bones during childhood–New cartilage is continuously formed–Older cartilage becomes ossified•Cartilage is broken down• Enclosed cartilage is digested away,

opening up a medullary cavity•Bone replaces cartilage through the

action of osteoblasts

Bone Growth (Ossification)• Bones are remodeled and lengthened until

growth stops–Bones are remodeled in response to two

factors•Blood calcium levels•Pull of gravity and muscles on the

skeleton–Bones grow in width (called appositional

growth)

Types of Bone Cells

• Osteocytes—mature bone cells• Osteoblasts—bone-forming cells• Osteoclasts—bone-destroying cells–Break down bone matrix for remodeling

and release of calcium in response to parathyroid hormone

• Bone remodeling is performed by both osteoblasts and osteoclasts

Bone Fractures

• Fracture—break in a bone–Types of bone fractures•Closed (simple) fracture—break that

does not penetrate the skin•Open (compound) fracture—broken

bone penetrates through the skin• Bone fractures are treated by reduction and

immobilization

Repair of Bone Fractures

• Repair of Bone Fractures• Hematoma (blood-filled swelling) is formed• Break is splinted by fibrocartilage to form a

callus• Fibrocartilage callus is replaced by a bony

callus• Bony callus is remodeled to form a

permanent patch

Repair of Bone Fractures

The Axial Skeleton

• Forms the longitudinal axis of the body• Divided into three parts–Skull–Vertebral column–Bony thorax

The Skull

• Two sets of bones–Cranium–Facial bones

• Bones are joined by sutures• Only the mandible is attached by a freely

movable joint

Paranasal Sinuses

• Hollow portions of bones surrounding the nasal cavity

• Functions of paranasal sinuses–Lighten the skull–Give resonance and amplification to voice

The Hyoid Bone

• The only bone that does not articulate with another bone

• Serves as a moveable base for the tongue• Aids in swallowing and speech

The Fetal Skull

• The fetal skull is large compared to the infant’s total body length

• Fontanels—fibrous membranes connecting the cranial bones–Allow the brain to grow–Convert to bone within 24

months after birth

The Vertebral Column

• Each vertebrae is given a name according to its location– There are 24 single vertebral bones separated

by intervertebral discs• Seven cervical vertebrae are in the neck • Twelve thoracic vertebrae are in the chest

region• Five lumbar vertebrae are associated with

the lower back


• Nine vertebrae fuse to form two composite bones– Sacrum– Coccyx

• The spine has a normal curvature– Primary curvatures are the spinal curvatures of

the thoracic and sacral regions - present from birth

– Secondary curvatures are the spinal curvatures of the cervical and lumbar regions - develop after birth


• Sacrum - formed by the fusion of five vertebrae

• Coccyx–Formed from the fusion of three to five

vertebrae–“Tailbone,” or remnant of a tail that other

vertebrates have

The Bony Thorax

• Forms a cage to protect major organs• Consists of three parts–Sternum–Ribs • True ribs (pairs 1–7)• False ribs (pairs 8–12)• Floating ribs (pairs 11–12)

–Thoracic vertebrae

The Appendicular Skeleton

• Composed of 126 bones–Limbs (appendages)–Pectoral girdle–Pelvic girdle

The Pectoral (Shoulder) Girdle

• Composed of two bones–Clavicle—collarbone–Scapula—shoulder blade

• These bones allow the upper limb to have exceptionally free movement

Bones of the Upper Limbs

• Humerus–Forms the arm–Single bone

• The forearm has two bones–Ulna - medial bone in anatomical position–Radius - lateral bone in anatomical

position

Bones of the Upper Limbs

• The hand–Carpals—wrist –Metacarpals—palm–Phalanges—fingers

Bones of the Pelvic Girdle

• Formed by two coxal (ossa coxae) bones• Composed of three pairs of fused bones–Ilium–Ischium–Pubis

Bones of the Pelvic Girdle

• The total weight of the upper body rests on the pelvis

• It protects several organs–Reproductive organs–Urinary bladder–Part of the large intestine

Gender Differences of the Pelvis

• The female inlet is larger and more circular• The female pelvis as a whole is shallower, and

the bones are lighter and thinner• The female ilia flare more laterally• The female sacrum is shorter and less curved• The female ischial spines are shorter and farther

apart; thus the outlet is larger• The female pubic arch is more rounded because

the angle of the pubic arch is greater

Gender Differences of the Pelvis

Bones of the Lower Limbs

• The thigh has one bone–Femur - the heaviest, strongest bone in

the body• The lower leg has two bones–Tibia• Shinbone• Larger and medially oriented

–Fibula - thin and sticklike

Bones of the Lower Limbs

• The foot–Tarsals • Two largest tarsals–Calcaneus

(heelbone)–Talus

–Metatarsals—sole–Phalanges—toes

Arches of the Foot

• Bones of the foot are arranged to form three strong arches–Two longitudinal–One transverse

Joints

• Articulations of bones• Functions of joints–Hold bones together–Allow for mobility

• Ways joints are classified–Functionally–Structurally

Functional Classification of Joints

• Synarthroses - immovable joints• Amphiarthroses - slightly moveable joints• Diarthroses - freely moveable joints

Structural Classification of Joints

• Fibrous joints - generally immovable• Cartilaginous joints - immovable or slightly

moveable• Synovial joints - freely moveable

Fibrous Joints

• Bones united by fibrous tissue• Example:–Sutures–Syndesmoses•Allows more movement than sutures• Example: Distal end of tibia and fibula

Cartilaginous Joints

• Bones connected by cartilage• Example:–Pubic symphysis–Intervertebral joints

Synovial Joints

• Articulating bones are separated by a joint cavity

• Synovial fluid is found in the joint cavity

Features of Synovial Joints

• Articular cartilage (hyaline cartilage) covers the ends of bones

• A fibrous articular capsule encloses joint surfaces

• A joint cavity is filled with synovial fluid• Ligaments reinforce the joint

Structures Associated with the Synovial Joint

• Bursae—flattened fibrous sacs–Lined with synovial membranes–Filled with synovial fluid–Not actually part of the joint

• Tendon sheath• Elongated bursa that wraps around a

tendon

Inflammatory Conditions Associated with Joints

• Bursitis—inflammation of a bursa usually caused by a blow or friction

• Tendonitis—inflammation of tendon sheaths

• Arthritis—inflammatory or degenerative diseases of joints– Over 100 different types– The most widespread crippling disease in the

United States

Clinical Forms of Arthritis

• Osteoarthritis–Most common chronic arthritis–Probably related to normal aging

processes


• Rheumatoid arthritis–An autoimmune disease—the immune

system attacks the joints–Symptoms begin with bilateral

inflammation of certain joints–Often leads to deformities


• Gouty arthritis–Inflammation of joints is caused by a

deposition of uric acid crystals from the blood–Can usually be controlled with diet

Developmental Aspects of the Skeletal System

• At birth, the skull bones are incomplete• Bones are joined by fibrous membranes

called fontanels• Fontanels are completely replaced with

bone within two years after birth

Skeletal Changes Throughout Life

• Fetus–Long bones are formed of hyaline

cartilage–Flat bones begin as fibrous membranes–Flat and long bone models are

converted to bone


• Birth - fontanels remain until around age 2• Adolescence - epiphyseal plates become

ossified and long bone growth ends• Size of cranium in relationship to body– 2 years old—skull is larger in proportion to the body

compared to that of an adult– 8 or 9 years old—skull is near adult size and

proportion– Between ages 6 and 11, the face grows out from the

skull


• Curvatures of the spine–Primary curvatures are present at birth

and are convex posteriorly –Secondary curvatures are associated

with a child’s later development and are convex anteriorly–Abnormal spinal curvatures (scoliosis

and lordosis) are often congenital


• Osteoporosis– Bone-thinning disease afflicting • 50% of women over age 65 • 20% of men over age 70

– Disease makes bones fragile and bones can easily fracture

– Vertebral collapse results in kyphosis (also known as dowager’s hump)

– Estrogen aids in health and normal density of a female skeleton

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Skeletal System